orchestration api tests remove duplicate client assignment

Many tests are setting cls.orchestration_client but it's
already assigned in the superclass setUpClass.

Change-Id: Iac5477561d4256d63d3c592d3dbb05a4a359b323
Merge "orchestration api tests remove duplicate client assignment"
Merge commit 'refs/changes/65/81565/4' of git://gold.eng.hq.xensource.com/git/github/openstack/tempest into tmpbranch